4 replies to this topic

[Richi_S]

Well, here we go, my first Atari 2600 programm.

This programm draws a starfield of 30 stars (Balls) moving horizontally over the screen.
Various star colors and star speeds implemented.
Unfortunately there is a glitch, the stars are jumping foreward at X-position 75.
This must be some problem with the Tia ball movement.
The Star X-position registers show their designated behavior. I checked this with Stella.
Out of frustration I wrote the vertical positioning tables by my own (Rev. 2).
Then playing around with the positions (Rev. 3) not causing any improvement.
Can you give me assistance on that?.

 starfield.bin   4K   137 downloads
 starfield.txt   10.51K   112 downloads

[Omegamatrix]

Hi Richi_S,


Nice demo. I think it's neat. The jump you are noticing is a timing error. The error occurs because your "Horizontal_move_fine_table" data table crosses over a page boundary. This is bad because it will sometimes add an extra cycle to your critically timed positioning routine. To fix this problem make sure that it all falls within a page. I put ORG $F100 before it, and then it worked fine.



Happy programming
Jeff

[Richi_S]

Thank you Jeff!

Now it works fine!
 starfield.bin   4K   132 downloads
 starfield.txt   10.43K   108 downloads

[mos6507]

Nice demo. Any chance of using it in a game, like a horizontal shooter?

[grafixbmp]

That might be great for a drop-in sequence for an R-Type game.